President Barack Obama and other leaders have issued statements on the passing of one of the most influential figures in politics.

"Arlen Specter was always a fighter," the president said. "From his days stamping out corruption as a prosecutor in Philadelphia to his three decades of service in the Senate, Arlen was fiercely independent – never putting party or ideology ahead of the people he was chosen to serve. He brought that same toughness and determination to his personal struggles, using his own story to inspire others. When he announced that his cancer had returned in 2005, Arlen said, "I have beaten a brain tumor, bypass heart surgery and many tough political opponents and I'm going to beat this, too." Arlen fought that battle for seven more years with the same resolve he used to fight for stem-cell research funding, veterans health, and countless other issues that will continue to change lives for years to come. Michelle and I send our thoughts and prayers to Joan and the rest of the Specter family."

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Former Pennsylvania Gov. Ed Rendell also shared his thoughts on Specter, saying he was "a mentor, colleague and a political institution." On a personal level, he said, Specter was "my first boss." Rendell served as an assistant prosecutor when Specter was Philadelphia's district attorney. Rendell also called Specter "a champion for veterans across our state and beyond" and said he "will be deeply missed." Rendell went on to say that Specter did more than anyone for the people of Pennsylvania "with the possible exception of Benjamin Franklin."

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"Jill and I are deeply saddened," said Vice President Joe Biden. "Arlen Specter was a great senator who lived his life the way he died, with dignity and courage. He was my friend and I admired him a great deal.

"For over three decades, I watched his political courage accomplish great feats and was awed by his physical courage to never give up. Arlen never walked away from his principles and was at his best when they were challenged.

"Jill and I are thinking of Joan at the moment – she was an incredible partner through his life journey. Our hearts go out to Shanin and Stephen and all who were deeply touched by his life."

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“I am deeply saddened to learn that my friend Arlen Specter has passed away," said U.S. Sen. Bob Casey, D-Pa. "I had the honor and privilege of working with him in the U.S. Senate on behalf of the people of Pennsylvania. Arlen was a statesman and a problem solver who was able to work with Democrats and Republicans in the best interest of our Commonwealth and our Country. Arlen fought cancer courageously and his enduring legacy of support for the National Institutes of Health will help countless Americans as they battle cancer and other ailments. My thoughts and prayers are with Joan, Shanin, Stephen and his entire family.”

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“A man of sharp intelligence and dogged determination, Sen. Specter dedicated his life to public service and the commonwealth of Pennsylvania," said U.S. Sen. Pat Toomey, R-Pa. His impact on our state and public policy will not be forgotten. My wife Kris and I send our thoughts and prayers to Joan and the entire Specter family.”

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“For more than five decades, Arlen Specter lived a life devoted to public service on behalf of the people of Pennsylvania and the United States," said Pa. Gov. Tom Corbett. "Pennsylvania has lost a political figure whose career stretched from Philadelphia's City Hall to the chambers of the U.S. Senate. We are saddened to hear of his death.”

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"Serving with Senator Specter for more than a decade, I can say without a shadow of a doubt that he was a fighter, and his commitment to public service was admirable," said former U.S. Sen. Rick Santorum, R-Pa. "Karen and I extend our deepest sympathies and prayers to the entire Specter family as they mourn their loss."

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"Arlen Specter was a dedicated public servant and tireless advocate for Pennsylvania," said U.S. Rep. Jim Gerlach, R-Pa. 6th District. "He was always willing to work with every member of the Pennsylvania delegation to address the needs of the communities we serve and the people we are privileged to represent. Senator Specter was a helpful partner in my efforts to honor the service of our veterans and the sacrifice of their families with the opening of a veterans’ cemetery in southeastern Pennsylvania. We also collaborated on the Chester County Public Safety Training Center project to ensure emergency responders would receive the very best training to save lives and keep themselves safe. A skilled prosecutor and legislator, Senator Specter never shied away from vigorous debates even with members of his own political party. I would like to offer sincere condolences to the entire Specter family."

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"Today, Saundy and I join Pennsylvanians in mourning the loss of a dedicated public servant," said Tom Smith, R-candidate for U.S. Senate. "Our thoughts and prayers are with Senator Specter's family and friends at this difficult time."

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"It is with deep sadness that I learned of the passing of former U.S. Senator Arlen Specter," said U.S. Rep. Charlie Dent, R-Berks Co./Lehigh Valley. Arlen Specter had a front row seat and was actively engaged in many significant issues of the past half century -- from the Warren Commission to Supreme Court nominations to the advancement of scientific research.

"A tough, fierce competitor, Arlen Specter courageously and tenaciously battled cancer as passionately as he advocated for the causes in which he believed. He will leave an everlasting legacy of service to the people of Pennsylvania and his commitment to medical research may well be remembered as his greatest public service achievement.

"My wife Pam and I send our heartfelt condolences to Joan and the entire Specter family."